Enhanced film forming ability of benzoxazine–urethane hybrid polymer network by sequential cure method

Abstract

Uniform copolymer films of benzoxazine resin (BA-a) and urethane prepolymer (PU) were prepared at various BA-a/PU mass ratios (100/0, 80/20, 60/40, 40/60, 20/80, and 0/100) via sequential cure method comprising of moisture cure and thermal cure steps. In the moisture cure step, Fourier Transform Infrared (FT-IR) spectra revealed the network formation between NCOterminated group and moisture to firstly produce PU solid film. Then in the thermal cure step, the change of tri-substituted benzene ring to tetra-substituted benzene ring was observed suggesting polybenzoxazine network formation in this step. Moreover, the spectra reveal that isocyanate groups in polyurethane structure could react with phenolic hydroxyl groups of BA-a to form biuret and allophanate groups. Dynamic mechanical analysis (DMA) confirms a synergistic behavior in glass transition temperature (T g ) of the alloys with the highest T g value of 275 C which is uniquely observed in these alloys obtained from traditionally thermal cure method. The proposed sequential cure method above is found to be highly useful for uniform coating or film casting process which lacks in traditional, low A-stage viscosity, benzoxazine resin.

Effects of polycaprolactone molecular weights on thermal and mechanical properties of polybenzoxazine

“…In addition, there is no by-product generated when curing that leads to no void in the final products. Alloying the brittle polybenzoxazine with other flexible monomers or polymers have been reported to enhance its crosslink density and mechanical properties in many blending systems such as benzoxazine/epoxy copolymer, 7,9,10 benzoxazine/ epoxy/phenolic ternary systems, [11][12][13] poly(benzoxazine-urethane) alloys, 8,[14][15][16] polybenzoxazine/dianhydride copolymer, 17 polybenzoxazine/ polycaprolactone blends. Moreover, it has been reported that the polymer possesses high thermal stability, high glass transition temperature (T g ) with low water absorption and near zero shrinkage or expansion.…”

Carbon fiber/epoxy vitrimer composite patch cured with bio‐based curing agents for one‐step repair metallic sheet and its recyclability

“…where T r is equal to Tg + 30 C, E' is the rubbery storage modulus (Pa) at T r , ρ is the crosslink density at room temperature (g cm À3 ), and R is the gas constant (8.314 m 3 Pa À1 K À1 ). 50…”

Dielectric and thermal behaviors of fluorine‐containing dianhydride‐modified polybenzoxazine: A molecular design flexibility

“…The obtained copolybenzoxazine at a weight ratio of 1/1 showed a relatively low dielectric constant of 2.36, compared with the value of about 3.56 for the polybenzoxazine without fluorine atoms in its structure. The second approach to enhancing the properties of polybenzoxazine is copolymer formations of the polybenzoxazine with other resins or polymers such as polyimide, polyurethanes, epoxy, and anhydride . Recently, Jubsilp et al .…”